1. Field of the Invention
The present invention relates to a spacer for use with an inhaler for dispensing powdered medicament. Such a spacer may be used to ensure that an effective dose of a discrete amount of medicament is dispensed by the inhaler by reducing drug particles above a predetermined size from the administered dose.
2. Discussion of the Related Art
Conventionally dry powder inhalers comprise three parts: a reservoir for solid medicament either in a dry powder form or in a form suitable for the generation of dry powder for delivery on demand; a metering device for delivery of consistent doses of medicament from the reservoir; and an outlet.
A patient inhaling through the outlet receives a metered dose of the medicament. Metered dose inhalers allow the patient to administer an accurate does of medicament when required. This is particularly useful during a sudden occurrence of respiratory difficulty, such as an asthma attack.
One problem with dry powder inhalers is to ensure that an effective dose of the medicament is delivered to the patient's lungs. Dispensed medicament particles tend to separate according to size under the influence of gravity and air currents. Smaller particles, for example less than 5-6 .mu.m in diameter, pass through the patient's oro-pharynx and enter the trachea, bronchi and lower airways where they are able to exert a therapeutic effect. Larger diameter particles are more likely to be deposited in the patient's oro-pharynx. Such oro-pharyngeal deposition is undesirable for a number of reasons. The patient may experience an unpleasant taste when particles alight on the mucosa. Furthermore the proportion of the dispensed dose inhaled which actually constitutes an effective dose is reduced. Moreover unwanted deposits of certain classes of compounds may cause undesirable side effects, eg a high incidence of Candida infections ("thrush") has been reported in association with the administration of corticosteroids.
In pressurised metered dose inhalers the larger droplets formed in the aerosol cloud have been separated out by providing a "large volume spacer" to allow these larger droplets to impinge on the spacer wall, evaporate or fall to the floor of the spacer. Such a "large volume spacer" is unsuitable for use with a powder inhaler where the patient's inspirational air flow withdraws the dose from the inhaler.
Alternatively impact surfaces have been used in order to break up the larger particles of medicament. However this requires a tortuous air path. This results in a bulky spacer and increases the inhalation force required for effective drug delivery. It is undesirable to impose a further burden on a patient who is already experiencing respiratory problems.